Apparatus and method for selecting optimum electrical power converter for variable power source

ABSTRACT

A method and apparatus use a programmable logic circuit to receive data representing environmental conditions such as irradiance, temperature, wind, snow, elevation, and the like, in a given location, to provide an input signal to a simulated variable power source which produces an output that approximates the output of a variable power source such as a photovoltaic panel that is subject to such environmental conditions. Power from the simulated variable power source is separately directed to each of a number of power converters and the efficiency of each power converter is tested to determine the optimum power converter for use with the variable power source in the given location.

BACKGROUND OF THE INVENTION

Electrical power from photovoltaic (PV) panels, wind turbines, and other sources of electrical power tends to be variable, depending upon real-time environmental conditions including temperature, luminescence, cloud cover, snow, wind velocity, and any other relevant factors. Electricity produced by such power sources must be converted from its native delivery state, such as direct current or variable frequency alternating current, to the U.S. standard of 60 Hz alternating current (or, in many countries, 50 Hz alternating current) before the power can be supplied to a power grid.

Power converters are available in a variety of capacities, and the efficiency of power conversion is an important factor in designing and installing new variable power sources. Thus, the choice of a power converter of a specific size or capacity may impact the efficiency of power generation and delivery, and presents challenges in the planning and design stages of any new variable power facility. Power sources located in different environments, such as, for example, southwest desert or forested mountainous regions, have different outputs that may be optimized by using a power converter whose energy yield and efficiency are greater than other power converters operating in the same environment. However, absent a side-by-side comparison, it is difficult to determine which of a variety of power converters will provide the optimal performance. What is needed is a way to determine what power converter will provide optimal efficiency for a specific power source type that will be installed in a predetermined location.

SUMMARY OF THE INVENTION

The invention is a simulation system that can be located in a laboratory or other similar testing facility, and that is programmed to provide a variable power source with inputs that are based on real-time environmental conditions for a given location. Inputs may include actual, recorded meteorological data (temperature, sunlight, wind speed and direction, etc.) which, in a preferred embodiment, would be provided to a programmable logic circuit (PLC), but could also be provided by a desktop computer, laptop computer, or other microprocessor device, or which may be based on manually programmed input. The PLC then controls a simulated variable power supply whose output is directed to one or more power converters. Measurements taken at the input and output for each power converter are analyzed to determine which power converter provides the greatest energy yield and efficiency. Simulations may be run in parallel, or may be run consecutively using the same programmed input data. The invention may be used in the planning of a site for the generation of electrical power, or may be used to upgrade the efficiency of existing sites.

In an alternative embodiment, historical data to be sent to simulated variable power source may be taken directly from an existing variable power source situated at the locale in which a power converter is to be used or upgraded. For example, if a PV variable power source has been installed at a location, and has provided power for some length of time, records representing the power output of the device can be used to generate an input to a simulated variable power source without the necessity of using recorded weather data. In this embodiment, the simulated variable power source may simply provide a power output to various power converters as previously described, and an analysis of the efficiency of each power converter may be used to select the optimum power converter to be used, or upgraded, for the locale.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts the problem to be solved as it relates to a photovoltaic solar panel.

FIG. 2 is a chart depicting parameters to be determined and supplied to the PLC as inputs to the variable power source.

FIG. 3 is a simplified schematic diagram of the invention using inputs from the chart depicted in FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates an installation having a variable power supply in the form of a photovoltaic (PV) panel 10 whose immediate electrical output is in the form of a direct current 14 of variable power. A power converter 12 receives direct current (DC) power 14 from the PV panel and converts it to 60 Hz alternating current (AC) power 16 before placing it on a transmission line or power grid 18.

FIG. 2 is a series of graphs spanning a 12-month period, and providing representative recorded values for such relevant parameters as windspeed 20, irradiance 22, and temperature 24. Other parameters may include snowfall, rainfall, and dust in locations in which these factors may affect the output of a PV panel. Measurements are taken over a relevant time period that, in a preferred embodiment, will exceed at least one year. In FIG. 2, the time scale 26 shows data extending over a 12-month period.

It should be noted that, while parameters relevant to a PV panel are shown and described, the invention is not so limited, but may encompass these and other parameters relevant to the output of other variable power sources such as, for example, wind turbines. In FIG. 2, historical data is used to program a PLC 30 which can mimic the weather data and apply algorithms to generate an input signal for a power source whose output can be modulated to conform to the input signal.

FIG. 3 depicts a simplified schematic diagram showing a variable power source 32 that receives an input signal from a PLC 30. The PLC may be a separate component, or may be integrated into the variable power source. The signal from the PLC is based upon weather parameters as previously noted, and causes the variable power source to provide more power, or less power, as indicated by the input signal. Power is supplied to the variable power source 32 through a transformer 34 connected to a power grid. Power from the variable power source 32 is the passed through a number of power converters 36, one at a time, and the power converter output 44 is received by either a load bank of resistors 46 or may be sent back to the power grid 48. In FIG. 3, a switch 52 is shown as a means for directing the output of the power converter being tested to a load bank of resistors 46 or to the power grid 48.

In either case, the input and output of the power converter are analyzed by metering equipment 50 that may include a potential transformer (PT) or a current transformer (CT), and the efficiency of the power converter being tested is compared with the efficiencies of other power converters to determine which power converter provides optimal efficiency under the weather parameters indigenous to the specified location where the data were gathered. The input and output of the power converter may include such parameters as voltage, current, power, phase, or any other electrical measurement necessary to assess the efficiency of the power converter. In FIG. 3, three inverters (marked I, II and III) are being compared. Input and output switches, 40 and 42, direct power from the variable power source 32 through each power converter separately, and measurements of each power converter's efficiency may be compared with that of the others. Although FIG. 3 shows three power converters which may be individually selected at the throw of a switch, a more likely deployment for evaluating the output of the power converters is a setup that tests one converter at a time. Converters would be tested days, weeks, or months apart and have their results compared. Such an analysis would produce accurate results, since the inputs were the same.

As this simulation and analysis can be done in a laboratory remote from the proposed or actual installation, and the most efficient power converter can be selected, this invention allows the design and efficiency to be determined before an installation or, in some cases, a retro fit or upgrade, takes place. Time, money, and resources may be enhanced where the invention is used.

As an alternative means of providing input to the variable power source, historically collected data may be manually entered into the system, and the most efficient power converter may be determined using such data.

Persons of ordinary skill in the art will understand that the invention has been shown and described in a number of embodiments, but is not restricted to only those embodiments and is limited only by the claims appended hereto. 

I claim:
 1. A method for selecting a power converter to be used with a variable power source, said method comprising the steps of: providing a variable power source; determining a location for said variable power source; recording weather parameters for said location, said parameters comprising at least air temperature; providing a simulated variable power source whose power output is responsive to an input signal; converting said weather parameters into a signal representing a power output from said variable power source when said weather parameters are present; applying said signal as an input signal to said simulated variable power source to cause the power output of said simulated variable power source to approximate the power output that would be produced by said variable power source when said weather parameters are present; connecting said simulated variable power source to a first power converter, measuring electrical parameters comprising at least voltage and amperage at the input and output of said first power converter, and determining the efficiency of said first power converter; substituting another power converter for said first power converter and repeating the step of connecting said simulated variable power source to a power converter, measuring electrical parameters comprising at least voltage and amperage at the input and output of said other power converter, and determining the efficiency of said other power converter; selecting a power converter based upon the results of efficiency comparisons.
 2. A method for selecting a power converter as claimed in claim 1 further comprising said simulated variable power source being connected to a power grid.
 3. A method for selecting a power converter as claimed in claim 1, further comprising directing the output of said first and other power converters to a load bank of resistors.
 4. A method for selecting a power converter as claimed in claim 1, further comprising directing the output of said first and other power converters to a power grid.
 5. A method for selecting a power converter as claimed in claim 1, said variable power output further comprising a photovoltaic panel.
 6. A method for selecting a power converter as claimed in claim 1, said variable power output further comprising a wind turbine.
 7. A method for selecting a power converter to be used with a variable power source, said method comprising the steps of: providing a variable power source; determining a location for said variable power source; recording data representing actual power output from said variable power source situated in said location; converting said data into a signal representing actual power output from said variable power source; applying said signal as an input to a simulated variable power source whose output is responsive to said signal to cause the power output of said simulated variable power source to approximate the power output that was actually produced by said variable power source; connecting said simulated variable power source to a first power converter, measuring electrical parameters comprising at least voltage and amperage at the input and output of said first power converter, and determining the efficiency of said first power converter; substituting another power converter for said first power converter and repeating the step of connecting said simulated variable power source to a power converter, measuring electrical parameters comprising at least voltage and amperage at the input and output of said other power converter, and determining the efficiency of said other power converter; selecting a power converter based upon the results of efficiency comparisons.
 8. A method for selecting a power converter as claimed in claim 7 further comprising said simulated variable power source being connected to a power grid.
 9. A method for selecting a power converter as claimed in claim 7, further comprising directing the output of said first and other power converters to a load bank of resisters.
 10. A method for selecting a power converter as claimed in claim 7, further comprising directing the output of said first and other power converters to a power grid.
 11. A method for selecting a power converter as claimed in claim 7, said variable power source further comprising a photovoltaic panel.
 12. Apparatus for selecting a power converter to be used with a variable power source, said apparatus comprising: a simulated variable power source whose output is responsive to an input signal; a plurality of power converters including a single power converter to be selected; historical data representing weather parameters including at least historical irradiance data and historical temperature data; a programmable logic circuit (PLC) programmed to receive said historical data and generate an input signal to said simulated variable power source; metering equipment for measuring and assessing the efficiency of each of said plurality of power converters; connection means for (i) providing said historical data to said PLC, (ii) sending said input signal from said PLC to said simulated variable power source, (iii) directing said output of said simulated variable power source to one of said plurality of power converters; and (iv) connecting said metering equipment to said input and said output of said one of said plurality of power converters; whereby, upon directing said output of said simulated variable power source to each of said plurality of power converters, and operating said metering equipment to determine the efficiency of each of said plurality of power converters, a most efficient power converter may be determined.
 13. Apparatus for selecting a power converter to be used with a variable power source as claimed in claim 12, further comprising connection means whereby said output from said one of said plurality of power converters is directed to a power grid.
 14. Apparatus for selecting a power converter to be used with a variable power source as claimed in claim 12, further comprising connection means whereby said output from said one of said plurality of power converters is directed to a load bank of resistors.
 15. Apparatus for selecting a power converter to be used with a variable power source as claimed in claim 12, further comprising connection means whereby said output from said one of said plurality of power converters is directed to a power grid.
 16. Apparatus for selecting a power converter to be used with a variable power source, said apparatus comprising: a simulated variable power source whose output is responsive to an input signal; a plurality of power converters including a single power converter to be selected; data representing actual power output from a variable power source; a programmable logic circuit (PLC) programmed to receive said data and generate an input signal to said simulated variable power source; metering equipment for measuring and assessing the efficiency of each of said plurality of power converters; connection means for (i) providing said historical data to said PLC; (ii) sending said input signal from said PLC to said simulated variable power source; (iii) directing said output of said simulated variable power source to one of said plurality of power converters; and (iv) connecting said metering equipment to said input and said output of said one of said plurality of power converters; whereby, upon directing said output of said simulated variable power source to each of said plurality of power converters, and operating said metering equipment to determine the efficiency of each of said plurality of power converters, a most efficient power converter may be determined.
 17. Apparatus for selecting a power converter to be used with a variable power source as claimed in claim 16, further comprising connection means whereby said output from said one of said plurality of power converters is directed to a power grid.
 18. Apparatus for selecting a power converter to be used with a variable power source as claimed in claim 16, further comprising connection means whereby said output from said one of said plurality of power converters is directed to a load bank of resistors.
 19. Apparatus for selecting a power converter to be used with a variable power source as claimed in claim 16, further comprising connection means whereby said output from said one of said plurality of power converters is directed to a power grid. 